To be compatible with a various types of fuel including liquid oil fuel such as fuel oil, diesel fuel and liquefied petroleum gas (LPG), and gas fuel such as natural gas and coal gas, a dual-fuel type gas turbine combustor capable of switching the fuel to be used between the oil fuel and the gas fuel has been known.
In a dual-fuel type gas turbine combustor, once the fuel to be used is switched to gas fuel from oil fuel, it is inevitable that the oil fuel remains in a passage (an oil fuel line) for introducing the oil fuel to a nozzle. This residual oil cokes from being exposed to a high temperature environment resulting from combustion of the gas fuel. This causes blockage of the nozzle. Even if the nozzle is not completely blocked, a fuel injection amount from the nozzle deviates from a desired value in some cases, which could result in generation of combustion oscillation, deviation of exhaust gas environmental regulation value (NOx amount, CO amount) from a regulation range, etc. Once there is failure such as blockage of the nozzle and the deviation from the desired value of the fuel injection amount, it is necessary to remove the nozzle where the failure took place to clean the nozzle. This requires the gas turbine to be shut down temporarily, missing a power generation opportunity.
Therefore, there is a purge technique proposed to drain residual oil from each system by purging a main oil fuel system and a pilot oil fuel system by water or gas in a time-sharing manner immediately after the fuel to be used is switched to gas fuel from oil fuel (e.g. Patent Literature 1).
It was thought that the above-mentioned failures caused by coking of the residual oil (blockage of the nozzle and deviation of the fuel injection amount from the desired value) could be prevented by the above purge technique, i.e. by purging immediately after the operation is switched to gas firing operation from oil firing operation so as to forcibly discharge the liquid oil fuel remaining in the oil fuel system (the residual oil prior to the coking).